When a combinational optimization problem is solved by sequential computation of a von Neumann computer which is mainly used at present, the computing time is known to exponentially increase relative to the number of variables. Hence, there is a demand for a high-speed computing apparatus that directly utilizes a physical phenomenon. The combinational optimization problem is known to be sometimes mapped to the energy minimization problem of a statistical model called an Ising model. In the Ising model to which the combinational optimization problem is mapped, the interactions between elements are not even. If there is a computing apparatus for solving the energy minimization problem of the Ising model at a high speed, a corresponding combinational optimization problem can be solved at a high speed.